Pyridine: N-oxide promoted hydrosilylation of carbonyl compounds catalyzed by [PSiP]-pincer iron hydrides

Article abstract of DOI:10.1039/d0dt00392a

Five [PSiP]-pincer iron hydrides 1-5, [(2-Ph2PC6H4)2HSiFe(H)(PMe3)2 (1), (2-Ph2PC6H4)2MeSiFe(H)(PMe3)2 (2), (2-Ph2PC6H4)2PhSiFe(H)(PMe3)2 (3), (2-(iPr)2PC6H4)2HSiFe(H)(PMe3) (4), and (2-(iPr)2PC6H4)2MeSiFe(H)(PMe3)2 (5)], were used as catalysts to study the effects of pyridine N-oxide and the electronic properties of [PSiP]-ligands on the catalytic hydrosilylation of carbonyl compounds. It was proved for the first time that this catalytic process could be promoted with pyridine N-oxide as the initiator at 30 °C because the addition of pyridine N-oxide is beneficial for the formation of an unsaturated hydrido iron complex, which is the key intermediate in the catalytic mechanism. Complex 4 as the best catalyst shows excellent catalytic performance. Among the five complexes, complex 3 was new and the molecular structure of complex 3 was determined by single crystal X-ray diffraction. A proposed mechanism was discussed.

Full text of DOI:10.1039/d0dt00392a

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10.1039/D0DT00392A.
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Number 10
14 March 2017
Pages 3073-3412
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DOI: 10.1039/D0DT00392A
Pyridine N-oxide promoted hydrosilylation of carbonyl compounds catalyzed by
[PSiP]-pincer iron hydrides
Guoliang Changa, Peng Zhanga, Wenjing Yanga, Shangqing Xiea, Hongjian Suna,
Xiaoyan Lia,*, Olaf Fuhrb, Dieter Fenskeb
______________________________________________
Abstract
Five [PSiP]-pincer iron hydrides 1 – 5, [(2-Ph2PC6H4)2HSiFe(H)(PMe3)2 (1), (2-
Ph2PC6H4)2MeSiFe(H)(PMe3)2 (2), (2-Ph2PC6H4)2PhSiFe(H)(PMe3)2 (3), (2-
(iPr)2PC6H4)2HSiFe(H)(PMe3) (4), and (2-(iPr)2PC6H4)2MeSiFe(H)(PMe3)2 (5)], were
used as catalysts to study the effects of pyridine N-oxide and electronic property of
[PSiP]-ligands on the catalytic hydrosilylation of carbonyl compounds. It was proved
for the first time that this catalytic process could be promoted with pyridine N-oxide as
initiator at 30 oC because the addition of pyridine N-oxide is beneficial for the formation
of unsaturated hydrido iron complex, which is the key intermediate in the catalytic
mechanism. Complex 4 as the best catalyst shows excellent catalytic performance.
Among the five complexes, complex 3 was new and the molecular structure of complex
3 was determined by single crystal X-ray diffraction. A proposed mechanism was
discussed.
______________________________________________
a School of Chemistry and Chemical Engineering, Key Laboratory of Special
Functional Aggregated Materials, Ministry of Education, Shandong University,
Shanda Nanlu 27, Jinan 250100, China
bInstitut für Nanotechnologie (INT), Karlsruher Nano-Micro-Facility (KNMF),
Karlsruher Institut für Technologie (KIT), Hermann-von-Helmholtz-Platz 1,
Eggenstein-Leopoldshafen 76344, Germany
† Electronic supplementary information (ESI) available: The table of selected
1
31
13
crystallographic data and original IR, H NMR, P NMR, and C NMR spectra of
complex 3 and catalytic products. For ESI and crystallographic data in CIF or other
electronic format see DOI: XXXXXXX
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Introduction
The homogeneous hydrosilylation catalysis for reduction of carbonyl compounds as a
significant route to synthesize organic alcohols attracts extensive investigation in
laboratory, academic field and industrial settings.1 It was reported in the past decade
that low-cost and environment friendly iron complexes as the catalysts could be used
in the reduction of aldehydes, ketons and the other unsaturated species.2-3 The
development on iron-catalyzed hydrosilylation reactions of carbonyl bonds was well
summarized in the review articles.4-6 The pioneering work for the first asymmetric iron-
catalyzed hydrosilylation of acetophenone by Brunner was reported in 1990.7
Nishiyama and Furuta disclosed that the combination of ferrous acetate and multi-
nitrogen-based ligands could efficiently catalyze hydrosilylation of ketones to give the
corresponding alcohols in high yields including asymmetric catalysis.8 In 2010,
Nishiyama reported the synthesis of chiral alcohols from aldehydes catalyzed by a
combination of iron(II) acetate and chiral bis(oxazolinylphenyl)amine ligands.9 Guan
and co-workers in 2011 disclosed the hydrosilylation reaction of a variety of aldehydes
and ketones with the iron hydrido complexes bearing the [PCP]-pincer ligands as
catalysts.10 Sortais described several iron complexes which catalyzed the
hydrosilylation of aldehydes and ketones upon visible light activation in 2012.11 In 2014,
the group of Guan used cationic iron complexes as the catalysts to increase catalytic
activity toward the hydrosilylation reduction of aldehydes and ketones.12 In 2018, our
group also investigated the reduction of aldehydes and ketones with iron hydrides
bearing a [PPP]-pincer ligand as catalysts.13 In addition, the design of catalysts played
an important role in the activity and selectivity for the reduction processes. Driess found
that iron complexes bearing silicon-based ligands could also be used as catalysts for
hydrosilylation of carbonyl compounds.14-15 It has been proved that the transition metal
complexes bearing phosphine-based [PSiP]-pincer silyl ligands as versatile pre-
catalysts could be used in the reduction of unsaturated compounds in recent years. The
main reason for such remarkable reactivity and catalytic activity of the [PSiP]-pincer
silyl metal complexes is that ligands have potent σ-donating characters and strong
2

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16
trans-influence in transition-metal chemistry. Furthermore, these two strategies can
promote the formation of electron-rich and coordinatively-unsaturated complexes.17
In the past few years, we reported that some hydrido iron complexes could catalyze
hydrosilylation of carbonyl compounds between 50 – 70 oC.13 Until now, in our reported
work, the catalytic mechanism catalyzed by iron hydrides was not experimentally
verified. Inspired by the catalytic mechanism reported by Nikonov,18 we consider that
the formation of unsaturated hydrido iron species formed via dissociation of the PMe3
ligand for our catalytic systems should be the first step in the related catalytic
mechanism. Therefore, we guess that the catalytic reaction could be also promoted by
taking measures to promote the dissociation of PMe3 ligands. With this assumption we
add pyridine N-oxide as initiator to enhance the dissociation of PMe3 due to the
production of stable O=PMe3. In addition, in order to compare the catalytic activities
of complexes with different groups, in this paper five hydrido [PSiP]-pincer iron
complexes 1 – 5 were synthesized (Figure 1). Among them, complex 3 was new and
was completely characterized and the molecular structure of 3 was determined by single
crystal X-ray diffraction. It has been confirmed for the first time that the catalytic
reactions with complexes 1 – 5 as catalysts could be significantly promoted with the
addition of pyridine N-oxide as initiator because this is beneficial to the formation of
coordinatively-unsaturated hydrido iron species by the reaction of PMe3 with pyridine
N-oxide. To our delight, the catalytic reactions could be realized in good to excellent
yields even at 30 oC. In 2013 we reported that complex 2 could be used as catalyst for
the hydrosilylation of carbonyl compounds at 60 oC.19 It is obvious that the addition of
pyridine N-oxide decreased the reaction temperature significantly. This result indicates
that the formation of unsaturated hydrido iron intermediate via dissociation of ligand is
the first and key step in the catalytic mechanism. Complex 4 shows the best catalytic
activity among the five complexes.
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Figure1 [PSiP]-pincer iron(II) silyl hydrides 1 – 5
Results and Discussion
Synthesis and characterization of complexes 1 - 5
The synthesis and characterization of complexes 1, 2, 4 and 5 were realized
according to the literature method.19-21 Complex 3 was synthesized by the reaction of
Fe(PMe3)4 with [PSiP]-pincer preligand, (2-Ph2PC6H4)2SiPhH (Scheme 1).
Scheme 1 Preparation of complex 3
In the IR spectrum of complex 3, the typical vibration (2134 cm-1) of the Si–H bond
of the preligand, (2-Ph2PC6H4)2SiPhH, disappeared while the ν(Fe–H) stretching band
was found at 1837 cm-1. The hydrido resonance in the 1H NMR spectrum of complex 3
appeared at -17.35 ppm as “tdd” peak with the coupling constant JPH = 71.4, 25.8, 6.9
Hz. Three different phosphorus signals at 1.3, 5.2 and 88.8 ppm appeared in the integral
ratio of 1 (PMe3) : 1 (PMe3) :2 (-PPh2) in the 31P NMR spectrum of 3. Meanwhile, X-
ray diffraction was used to confirm the octahedral configuration of complex 3 (Figure
2). The crystallographic data for complex 3 was listed in Table S1. In the molecular
structure of 3, Fe1-P3 bond length (2.2629(6)Å) is longer than the other three Fe-P
bonds (Fe1-P1 = 2.1970(3); Fe1-P1a = 2.1970(3) and Fe1-P2 = 2.2344(6) Å) due to the
strong trans-influence of the Si atom.
4

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Figure 2 Molecular structure of complex 3
Pyridine N-oxide promoted catalytic performance of iron(II) hydrides 1 - 5 for
hydrosilylation of aldehydes and ketones
In 2013 we initially confirmed that complex 2 could efficiently catalyze
hydrosilylation of carbonyl compounds at 60 oC.19 On this basis, in order to verify that
the formation of coordinatively-unsaturated hydrido iron species is the key step we
selected complexes 1 – 5 as catalysts and pyridine N-oxide as initiator to study catalytic
hydrosilylation of carbonyl compounds. Meanwhile, the effect of substituent groups of
the ligands on catalytic activity of the five complexes was also explored.
Initially, benzaldehyde as a model substrate was studied to evaluate the catalytic
activity of complexes 1 – 5 (Table 1). According to our early experience we used THF
as solvent and (EtO)3SiH as the reducing agent. From Table 1 we know that
o
benzaldehyde has no conversion without catalyst (entry 1, Table 1). At 30 C with 1
mol% of catalyst loading the five iron complexes have the conversion only between 9
– 29% within 6 h (entries 2 – 6, Table 1). Under this condition both complex 4 and 5
have better catalytic activity (entries 5 – 6, Table 1). It is surprising that, with the
addition of pyridine N-oxide the conversions reached between 32 – 98 % under the
same conditions (entries 7 – 11, Table 1). Among the five complexes, complex 4 is the
best catalyst and the yield increased from 25% (without pyridine N-oxide) to 98% (with
pyridine N-oxide) (entries 5 and 10, Table 1). The addition of pyridine N-oxide greatly
facilitates the dissociation of PMe3 with the formation of stable phosphine oxide. These
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results indicate that, as we expected, the dissociation of PMe3 ligand to form the active
coordinatively unsaturated hydrido iron intermediate is the first step. Obviously, it is
also rate-determining step. Additionally, electron-donating isopropyl group is beneficial
for the dissociation of PMe3 ligand and the formation of the active coordinatively
unsaturated intermediate. Compared to complex 5, it is clear that the coordinatively
unsaturated intermediate of complex 4 is more active because the tetra-coordinate
iron(II) intermediate is not stable. However, if the amount of pyridine N-oxide was
declined to 1 mol% from 5 mol%, the conversion declined sharply (entry 12, Table 1).
When the amount of pyridine N-oxide was increased to 10 mol%, the conversion of the
reaction remained almost unchanged (entry 13, Table 1). When the reaction time was
reduced to 4h or 2h, the conversion was declined significantly (entries 14 - 15, Table
1). When the reaction time was extended to 8h, the conversion could not be improved
significantly (entry 16, Table 1). Therefore, the conclusion is that the addition of
pyridine N-oxide can significantly improve the yields of the reaction only at 30 oC.
It was proved that the hydrosilylation of acetophenone could also be significantly
o
promoted by the addition of pyridine N-oxide at 50 C (entries 1 – 2, Table 2). The
reaction temperature is higher than that in Table 1 because ketones are less reactive
than aldehydes. However, the catalytic temperature of hydrosilylation of ketones (at 50
o
oC) is still lower than that in the literature.11 When the reaction time at 50 C was
shortened to 4h, the conversion decreased significantly (entry 3, Table 2). If the
reaction temperature was 30 oC, the conversion declined sharply although the reaction
time was extended to 12 h (entries 4 – 5, Table 2).
More aldehydes with different substituents at the phenyl rings were selected as the
substrates to extend the scope of this catalytic system under the optimized catalytic
condition (Table 3). It was found that this catalytic system is tolerant to both electron-
withdrawing groups and electron-donating groups at the phenyl rings. The alcohols
with either mono-substituted or bis-substituted and either ortho-substituted or para-
substituted halogen groups were obtained from their corresponding aldehydes in the
high yields. Furthermore, the alcohols with halogen groups at para-position were
formed in higher yields due to the small steric effect. The alcohols containing strong
6

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electron-withdrawing group, such as –NO2 and -CN, were produced in good yields
while the aldehydes with the electron-donating substituents, such as –Me and MeO-,
seemed to render the reaction poorer. The aliphatic alcohol (as 2-phenylethanol) was
also isolated in good yield in this system. The heterocyclic alcohols also had good yields.
Meanwhile, the yield of 1-naphthylmethanol was satisfactory, too. Compared with the
previous reports, the bright spot of this catalytic system is the significant reduction of
catalytic reaction temperature caused by the addition of pyridine N-oxide.
Table 1. Catalytic activity of 1 – 5 for hydrosilylation of benzaldehydea
Catalyst
loading
Pyridine N-
oxide
Time
(h)
Conv.
(%)
Entry
Catalyst
1
2
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
5
0
0
0
0
0
5
5
5
5
5
1
10
5
5
5
6
6
6
6
6
6
6
6
6
6
6
6
6
4
2
8
0
1
1
2
3
4
5
1
2
3
4
5
4
4
4
4
4
13
19
9
3
4
5
25
29
52
59
32
98
85
82
99
90
77
99
6
7
8
9
10
11
12
13
14
15
16
a Reaction conditions: benzaldehyde (1.0 mmol), (EtO)3SiH (1.2 mmol) and n-dodecane (internal
standard)(1.0mmol), 2mL THF, 30 oC.
Table 2. Catalytic activity of 4 for hydrosilylation of acetonphenonea
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Conv.
pyridine N-oxide
T
Time
Entry
1
2
3
4
5
0
5
5
5
5
50
50
50
30
30
6
6
41
89
66
47
62
4
6
12
a Reaction conditions: acetonphenone (1.0 mmol), 4 (0.01 mmol), pyridine N-oxide, (EtO)3SiH
(1.2mmol) and n-dodecane (internal standard) (1.0 mmol), 2mL THF.
Table 3. Catalytic hydrosilylation of carbonyl compounds with 4 as catalysta
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CH2OH
CH2OH
CH2OH
CH2OH
F
Cl
Br
Cl
88%
86%
95%
85%
87%
96%
CH2OH
F
CH2OH
Br
CH2OH
Cl
CH2OH
Cl
83%
Cl
80%
CH2OH
CH2OH
CH2OH
CH2OH
Cl
NO2
NC
MeO
77%
82%
82%
84%
88%
S
CH2OH
CH2OH
O
CH2OH
CH2OH
CH2OH
78%
74%
85%
80%
OH
OH
OH
OH
OH
OH
F
Cl
86%b
OH
80%b
87%b
89%b
OH
N
MeO
76%b
80%b
92%b
78%b
OH
OH
OH
OH
Cl
90%
86%
87%
OH
CH2OH
5
77%
73%
81%
a Reaction conditions: substrate (1.0 mmol), (EtO)3SiH (1.2 mmol), 4 (0.01mmol) and pyridine N-
oxide (0.05 mmol) in 2 mL THF at 30°C for 6 h in isolated yields.
b
For ketones: substrate (1.0 mmol), (EtO)3SiH (1.2 mmol), 4 (0.01mmol) and pyridine N-oxide
(0.05 mmol) in 2 mL THF at 50°C for 6 h.
Compared to aldehydes, the reduction of ketones is more difficult and required
more stringent reaction conditions. With pyridine N-oxide as initiator the
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o
hydrosilylation of ketones was realized in good yields at 50 C within 6h. From Table
3 it can be concluded that the secondary alcohols could be isolated from the related
ketones in moderate to excellent yields. The yield of alcohol with electron-donating
substituent (MeO-) is lower than those of the alcohols with electron-withdrawing
groups (F- and Cl-). The heterocyclic ketone (2-acetyl pyridine) was transferred to the
related alcohol in excellent yield. 2-Acetonaphthone and benzophenone are also
suitable for this catalytic system. We have tested the reaction of benzaldehyde and
acetophenone (1:1) with complex 4 as catalyst and (EtO)3SiH as hydrogen source at 30
oC. The conversion of benzaldehyde is 97% while the conversion of acetophenone is
only 2%. The results show that aldehyde group is easier to be reduced than ketone group.
The selective hydrogenation reduction of the C=C and C=O bond in α,β-
unsaturated aldehydes or ketones is of great importance in organic synthesis. To our
delight, this catalytic system has good selectivity for reduction of ,-unsaturated
aldehydes and ketones (Table 3). The cinnamyl alcohol was obtained via the reduction
of the corresponding cinnamaldehydes. In this process the C=C bond remained
unchanged. Meanwhile, 4-chloro cinnamyl alcohol and α-hexyl cinnamyl alcohol were
obtained in excellent yields. It must be emphasized that α-bromo cinnamaldehyde
reacted with (EtO)3SiH to afford 3-phenyl-2-propyn-1-ol via the elimination of HBr
(77%, Table 3). In addition, α,β-unsaturated ketone is also applicable to this system and
1,3-diphenyl-2-propenol was isolated in the yield of 73%.
Mechanism Discussion
10

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Scheme 2 Proposed mechanism with complex 4 as catalyst for hydrosilylation of
carbonyl compounds
Based on our experimental results and literature reports,18 we proposed a catalytic
mechanism with complex 4 as catalyst for hydrosilylation of carbonyl compounds
(Scheme 2). At the beginning, in the presence of pyridine N-oxide, a
trimethylphosphine ligand was dissociated from complex 4 to form an active
intermediate 4a. The coordinatively unsaturated 4a combines with a substrate molecule
to form intermediate 4b. After that, the coordinate carbonyl group is inserted into the
Fe-H bond to afford intermediate 4c. In the presence of (EtO)3SiH, complex 4c can be
converted into an intermediate 4d with a four-membered ring [FeOSiH]. The silylation
product was formed by -metathesis reaction via 4d and the real catalyst 4a was
regenerated for next catalytic cycle. We have monitored the reaction between complex
4 and pyridine N-oxide using the in situ NMR and IR. We found the signal at 31.8 ppm
22
for O=PMe3 in the in situ 31P NMR and a new signal at -10.16 ppm for hydrido
hydrogen in the in situ 1H NMR. In addition, a novel vibration for Fe-H bond appeared
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-1
at 1937 cm in the in situ IR spectrum when pyridine N-oxide was added into the
solution of complex 4. We consider that these experimental results support the
formation of complex 4a.
Conclusion
Five [PSiP]-pincer silyl iron hydries 1 – 5 were used as catalysts for the hydrosilylation
of carbonyl compounds. It was proved for the first time that the addition of pyridine N-
oxide could greatly promote the catalytic reactions and reduce the reaction temperature
from 60 oC to 30 oC in the case of aldehydes. This result explains that the dissociation
of PMe3 to form the coordinatively unsaturated intermediate is an important step in the
catalytic process. Among complexes 1 – 5, complex 4 is the best catalyst in the presence
of pyridine N-oxide but complex 5 has almost similar activity as complex 4 without
pyridine N-oxide. The electron-donating groups (the isopropyl gropups at the P atom)
make complexes 4 and 5 more catalytically active. Among the five complexes, complex
3 was new and the molecular structure of complex 3 was determined by single crystal
X-ray diffraction. A proposed mechanism was discussed.
Experimental section
General procedures and materials
Standard vacuum techniques were used in the manipulations of volatile and
air-sensitive materials. Solvents were dried by known procedures and distilled
under nitrogen before use. Infrared spectra (4000 − 400 cm−1), as obtained from
Nujol mulls between KBr disks, were recorded on a Bruker ALPHA FT-IR
instrument. NMR spectra were recorded using Bruker Avance 300 MHz
spectrometers. GC was recorded on a Fuli 9790 instrument. Melting point was
measured in capillarie sealed under N2 and was uncorrected. Elemental analyses
were carried out on an ElementarVario EL III instrument. All the aldehydes,
ketones and α, β-unsaturated carbonyl compounds were purchased and used
without further purification. The purity of the triethoxysialne used is 95%, the
other 5% is tetraethoxysialne. The silanes were purchased from J&K scientific.
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[PSiP]-pincer preligand {bis[o-(diphenylphosphino)phenyl] phenylsilane},
Fe(PMe3)424 and complexes 1, 2, 4 and 19-21 were prepared according to literature
5
procedures.
Synthesis of hydrido iron(II) complex 3
At 0 °C, Fe(PMe3)4 (0.36 g, 1 mmol) in 25 mL toluene was added to a
solution of (2-Ph2PC6H4)2SiPhH (0.63 g, 1 mmol) in 35 mL of toluene in N2
atmosphere. The mixture was warmed to room temperature and the color of
solution has no obvious change. After stirred at room temperature for 24h, the
solution was evaporated to dryness at reduced pressure. The residue was washed
by two portions of 10 ml of cold n-pentane. Complex
3 (0.63 g, 0.75 mmol) was
isolated as an orange powder in a yield of 75%. Crystals suitable for X-ray
diffraction were obtained from n-pentane solution through recrystallization. dec.:
＞147 °C. Anal. Calc. for C48H52FeP4Si (836.77 g/mol): C, 68.90; H, 6.26. Found:
69.19; H, 6.15. IR (Nujol mull, cm-1): 3045 (Ar-H), 1837 (Fe-H), 1583 (C=C),
1
939 (PMe3). H NMR (300 MHz, C6D6, 300 K, δ/ppm): -17.55 (tdd, J = 71.4,
25.8, 6.9 Hz, 1H, Fe-H), 0.68 (d, J = 6.0 Hz PCH3, 9H), 1.07 (s , PCH3, 9H), 6.62
- 6.81 (m, 20H, Ar-H), 6.27 - 6.58 (m, 11H, Ar-H), 8.11 (d, J = 7.4 Hz, 2H).31P
NMR (121 MHz, C6D6, 300K, δ/ppm): 88.8 (t, J = 32.2 Hz, 2P, PiPr), 5.2 (q, J =
29.8 Hz, 1P, PMe3), 1.3 (q, J = 18.9 Hz, 1P, PMe3). 13C NMR (75 MHz, C6D6,
300K, δ/ppm) 157.08 (s, Ar-C), 151.61 (s, Ar-C), 142.53 (s, Ar-C), 136.13 (s,
Ar-C), 132.58 (t, J = 4.5 Hz, Ar-C), 131.61 (t, J = 9.7 Hz, Ar-C), 130.59 (s, Ar-
C), 127.91 (s, Ar-C), 125.58 (s, Ar-C), 125.70 (s, Ar-C), 125.46 (t, J = 3.0 Hz),
124.27 (s, Ar-C), 25.25 (dd, J = 1.5, 17.3 Hz, PMe3-C), 22.59 (dd, J = 2.3, 17.3
Hz, PMe3-C).
Single crystal X-ray diffraction
Bruker Apex II single crystal diffractometer was used with a Ga Kα radiation
(λ = 1.34143) and a CCD area detector. The structure was solved using the
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25
charge-flipping algorithm, as implemented in the program SUPERFLIP and
refined by full-matrix least-squares techniques against F2 (SHELXL)26 through
the OLEX interface.27 All non-hydrogen atoms were refined anisotropically and
all hydrogen atoms except for those of the disordered solvent molecules were
placed using AFIX instructions. Appropriate restraints or constraints were
applied to the geometry and the atomic displacement parameters of the atoms.
CCDC-1936211 (3) contains the supplementary crystallographic data for this
paper. Copies of the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
Representative experimental procedure of catalytic reduction of aldehydes and
ketones
A 25 mL Schlenk tube was charged with a mixture of PhCHO (1.0 mmol),
HSi(OEt)3 (1.2 mmol), pyridine N-oxide (0,05 mmol) and complex
4 (0.01 mmol)
in 2 mL of THF. The reaction vessel was stirred at 30 °C for 6 h. The progress
of the reaction was monitored by GC. After cooling to the room temperature,
CH3OH (2 mL) and 10% NaOH (3 mL) were added to the tube. After stirring for
24 h at 60 °C, the product was extracted with Et2O (30 mL × 2). The combined
organic phases were dried over anhydrous NaSO4, filtered, and the solvent was
evaporated under reduced pressure. The product was purified by column
chromatography on silica gel (petroleum ether (60–90°C) / ethyl acetate 5:1, v/v)
to afford PhCH2OH as a colorless liquid.
Mechanism study
Conflicts of interest
There are no conflicts to declare.
14

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DOI: 10.1039/D0DT00392A
Acknowledgements
This work was supported by NSF China (Nos. 21971151/21572119) and the major basic
research projects of natural science foundation of Shandong province ZR2019ZD46.
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TOC
Pyridine N-oxide promoted hydrosilylation of carbonyl compounds catalyzed by
[PSiP]-pincer iron hydrides
Guoliang Changa, Peng Zhanga, Wenjing Yanga, Shangqing Xiea, Hongjian Suna,
Xiaoyan Lia,*, Olaf Fuhrb, Dieter Fenskeb




21 aldehydes
Isolated yields: 78 – 95%
Pyridine N-oxide as initiator
Lower reaction temperature: 30 oC
17